Only 1st group showing in frontend

I need your help once more with the groups, but now in the frontend.
After I made multipe groups, I can only really see the first one in the frontend, because it keeps using the full screen width and there is no room for others. A second group is pushed beneath, but only small parts of the letters are shown (the yellow in this image: harmoniesimpelveld.nl/feed.png ). Why is the group name/button so wide (does it come from global css)? How to override it and show the groups next to eachother as is nicely shown in the screenshots on your site?
Thanks for your help!